1,720,963 research outputs found
Performance evaluation of single-phase electricity meters types of electromechanical operating with non-linear loads
No full textO presente trabalho analisa o comportamento de medidores
monofásicos e trifásicos de energia elétrica dos tipos eletromecânico e eletrônico, quando os mesmos são submetidos a ambientes de cargas lineares e não-lineares, dos tipos residencial, comercial e industrial. Diferencia-se dos estudos correlatos principalmente por fazer uso de cargas reais encontradas no dia-a-dia, em vez de fontes de cargas eletrônicas como se tem observado no estado da arte. A comparação de resultados é feita tomando como base um
padrão de energia de alta precisão desenvolvido por meio de instrumentação virtualThis work analyzes the performance of single-phase and three-phase power meters, of the electromechanical and electronic types, when they are working with linear and nonlinear loads present in residence, commerce and
industry. It differs from related studies mainly for making use of actual loads encountered in day-to-day, rather than sources of electronic charges as has been observed in another papers. The comparison of results is made taking as
standard a meter power of high precision developed through virtual instrumentatio
Optimization process applied to investment risk analysis in power generation from renewable sources
No full textCoordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPESThis work presents a methodology for multiobjective optimization applied to risk analysis of investment in electricity generation from renewable sources. Analysis of hydro (large-scale and small-scale), wind, and photovoltaic energy is carried out considering the economic profile and demand of the investor. The methodology of risk analysis applies the Monte Carlo method to generate synthetic time series of the random variables. The investment analysis approaches are made for individual sources and also for different portfolios, using detailed modeling for the cash flow. The proposed mathematical modeling of multiobjective optimization takes into account aspects of commercialization, legislation, taxation, financing, and the investor's demand. The results provide information of the generation potential, statistical indicators of the Net Present Value and Modified Internal Rate of Return, as well as the Pareto frontiers. Thus, the investor can choose the best portfolio with hydro, wind and photovoltaic energy which satisfies their demand characteristics and their financial risk profile. Therefore, this work offers a valuable tool to support decision making and to contribute with the electric sector development.Este trabalho apresenta metodologia para otimização multiobjetivo aplicada à análise de risco de investimento em geração de energia elétrica a partir de fontes renováveis. Realiza-se análise das fontes hidrelétrica (grande e pequeno porte), eólica e solar fotovoltaica, considerando o perfil econômico e a demanda do investidor. Para cada fonte, será apresentada metodologia de análise de risco que utiliza modelos econométricos, com a aplicação do método de Monte Carlo, para geração de séries sintéticas das variáveis aleatórias. São apresentadas abordagens de análise de investimento considerando as fontes separadamente e também a formação de portfólios, utilizando detalhada modelagem para o fluxo de caixa. É proposta modelagem matemática de otimização multiobjetivo que considera os aspectos de comercialização no Ambiente de Contratação Livre e no Ambiente de Contratação Regulado, a legislação pertinente ao setor elétrico e o atendimento à demanda do projeto. Os resultados fornecem informações do potencial de geração, indicadores estatísticos das distribuições de probabilidade do Valor Presente Líquido, da Taxa Interna de Retorno Modificada e do Payback Descontado, e também fronteiras de Pareto com as soluções ótimas para investimento, onde o investidor poderá optar pela melhor carteira de investimento, composta por usinas PCH, eólica e solar fotovoltaica, que satisfaz suas características de demanda e seu perfil de risco financeiro. Portanto, este trabalho oferece ferramenta de apoio à tomada de decisão que visa contribuir para o desenvolvimento do setor elétrico
Intelligent control for maximum power generation in thermogenerators
No full textThis work presents a theoretical and experimental analysis of the physical connection and
intelligent control of DC-DC converters to the Seebeck thermoelectric generating system. The
methodology is based on the application of heuristic optimization methods for the tuning of
controllers, observing the transient and permanent responses. It is also developed
methodology using artificial neural network associated with the control in voltage mode,
necessary for the tracing of the maximum power of the thermogenerator. The computational
mathematical model of voltage converter, thermogenerator, controller based on the place of
roots, non-pre-phase systems and control techniques is described. The computational
simulations and and the practical tests are validated. The results indicate the efficiency of the
optimization methods in the tuning of the voltage controller and the best response times for
neural networks as a mechanism for tracking the maximum power.Este trabalho apresenta a análise teórica e experimental da conexão física e controle
inteligente de conversores CC-CC aplicados ao sistema termoelétrico de geração por efeito
Seebeck. A metodologia parte da aplicação de métodos de otimização heurística para sintonia
dos controladores observando as respostas em regime transitório e permanente. É
desenvolvida ainda metodologia utilizando rede neural artificial associada ao controle em
modo de tensão, necessário para o rastreamento da máxima potência do termogerador.
Descreve-se o modelo matemático computacional do conversor elevador de tensão, do
termogerador, do controlador em função do lugar das raízes, dos sistemas de fase não
mínima e das técnicas de controle. Valida-se as simulações computacionais em testes práticos
realizados em bancada. Os resultados apontam a eficiência dos métodos de otimização na
sintonia do controlador de tensão e os melhores tempos de resposta para redes neurais
artificiais como mecanismo de rastreamento da máxima potência
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Prediction methodology using system identification applied to time series
No full textCoordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPESThis work proposes a methodology that uses spectral analysis and system identification in order to fill gaps in time series. The methodology proposes the implementation of predictions
in time series of physical and chemical variables that are related with flood areas that are collected with no frequency. It is used predictive neural network with autoregressive model and classification neural network. Collected values are extracted from the original data set in order to later test and validate the proposed methodology. The results demonstrated the effectiveness of the methodology, which is able to predict the behavior of different variables using the previously recognized patterns in the time series.Este trabalho propõe metodologia que utiliza análise espectral em conjunto com modelo de identificação de sistema para preenchimento de lacunas em séries temporais. A metodologia propõe realizar previsão em séries temporais de variáveis físicas e químicas relacionadas as inundações com frequência de coleta variável. Utiliza-se rede neural artificial de previsão com modelo autorregressivo e rede neural classificatória. Valores coletados são armazenados para posteriormente testar e validar a metodologia proposta. Os resultados alcançados demonstram a eficácia da metodologia, que é capaz de prever o comportamento de diferentes variáveis utilizando os padrões reconhecidos previamente nas séries temporais
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